1. Field of the Invention
This invention relates to an electrostatic dust reduction system and a method for reducing dust, air contaminates, and airborne microorganisms in enclosed spaces, such as for example, poultry hatching cabinets, throwing rooms and controlled environment poultry rearing rooms, for example. The present invention reduces dust, microbial contamination and infection, especially of newly hatched chicks and poultry, including contamination and infection with human enteropathogenic organisms.
2. Description of the Related Art
The consumption of improperly prepared poultry products has resulted in numerous cases of human intestinal diseases. It has long been recognized that Salmonella spp. are causative agents of such diseases, and more recently Camplylobacter spp. As many as two million cases of salmonellosis occur annually in the United States (Stavrix et al., Journal of Food Protection, Volume 56, No. 2, 173-180, February, 1993); twice as many cases of campylobacteriosis are thought to occur (Krienberg et al., Food Technology, pages 77,80,81, and 98, July 1987). Both microorganisms may colonize poultry gastrointestinal tracts without any deleterious effects on the birds, and although some colonized birds can be detected, asymptomatic carriers can freely spread the microorganisms during production and processing, resulting in further contamination of both live birds and carcasses. Poultry serve as the primary reservoir for Salmonella and Campylobacter in the food supply (Jones et al., Journal of Food Protection, Volume 54, No. 4, 259-262, April 1991; Jones et al., Journal of Food Protection, Volume 54, No. 7, 502-507, July 1991). The intestinal contents of chickens may harbor up to 10.sup.7 Campylobacter and/or Salmonella per gram, and cross contamination during processing is frequent (Oosterom et al., Journal of Food Protection, Volume 46, No. 4, 339-344, April 1983). Studies have demonstrated that fecal material constitutes the major source from which edible parts of chickens are contaminated in processing plants. Therefore, to significantly reduce the level of contamination on processed poultry, pathogen-free birds must be delivered to the processing plant (Bailey, Poultry Science, Volume 72, 1169-1173, 1993).
Better control measures are needed to minimize the spread of these and other human enteropathogenic bacteria; and the most promising approach to achieve this end has been to decrease the incidence and level of colonization by these microorganisms in poultry gastrointestinal tracts. Hatching cabinets are known to be one of the primary sources for human enteropathogenic bacteria contamination of poultry. A considerable amount of dust is generated during the hatching process from the time of piping on day 20 through final hatching on day 21 of incubation. The dust is caused by the breaking up of egg shells and feather particles which are entrained into the air from the new chicks as they move around. Bailey et al (Poultry Science, Volume 71 (1):6; and Poultry Science, Volume 73(7), 1153-1157, 1994) demonstrated that a single salmonella contaminated egg could contaminate most of the eggs and newly hatched chicks in a hatching cabinet. This result suggests that extensive airborne transmission of the bacteria is possible since the typical hatching cabinet has several trays of fertile eggs on several different levels and on several different carts. Eggshell fragments, belting materials, and paper pads used in commercial hatcheries have also been shown to be sources of salmonella contamination (Cox et al, Poultry Sciences, Volume 69, 1606-1609, 1990).
Various intervention approaches have been taken in attempts to reduce airborne transmission of disease. Bailey et al (Poultry Science, Volume 75(2), 191-196, 1995) have demonstrated that chemical treatment of hatching cabinet air between day 18 and hatch can significantly reduce disease transmission caused by eggs which are internally contaminated with Salmonella. Treatments included UV-light, ozone, and fogging with hydrogen peroxide. The hydrogen peroxide treatment was the most effective in reducing salmonella on the shells, in the air, and in the chicks. Hopkins and Drury (Avian Diseases, Volume 15, 596-603, 1971) have demonstrated the ability of airborne diseases such as Newcastle disease virus (NDV) to be transmitted from groups of donor chickens to groups of susceptible chickens and the ability of high efficiency filters to interrupt this transmission. Madelin and Wathes (British Poultry Sciences, Volume 30, 23-37, 1989) found that a raised floor for broilers reduced respirable dust by a factor of 2 compared to dust in a room with broilers on deep liter. The airborne bacterial cfu counts were reduced by a factor of 3000 by the raised floors. Carpenter et al (British Poultry Sciences, Volume 27, 471-480, 1986) found that a recirculating high efficiency filter in a broiler house room reduced dust levels to about half that of an untreated room, and it reduced the concentration of airborne bacteria more than 100 fold.
Hugh-Jones et al (J. Hyg., Camb., Volume 71, 325-339, 1973) reported 63% of the NDV and 83-94% of total bacteria in poultry houses was found on particles &gt;6 microns. Thirty-six percent of the NDV was on 3-6 micron particles. Estola et al (Journal of Hygiene, Volume 83, 59-67, 1979) reported complete protection from airborne transmission of Newcastle disease virus by negative air ionizers but later studies (Mitchell and King, Avian Diseases, Volume 38, 725-732, 1994) have not been able to confirm their results. The studies of Mitchell and King (1994, supra), in controlled environment transmission cabinets, resulted in reductions in airborne transmission of NDV of up to 28% using negative air ionizers, but they hypothesized that higher reductions were possible with more efficient ion generators and ion distribution systems. Since previous reports indicate that most airborne bacteria and viruses are attached to larger particles, it is useful to look at dust reduction studies which did not involve microorganisms.
Hoenig et al (Foundrymens Soc. Transactions, Volume 84, 55-64, 1976) used a charged spray to reduce silica sand dust from 20 mg/m.sup.3 to 2 mg/m.sup.3 with positively charged water fog. Mitchell (ASAE Paper 954592, Chicago, Ill., 1995) reported improvements in decay rates of up to 42 fold for total inhalable particles using a negative air ionizer. Ionizers have been used to achieve dust reductions of up to 67% (Bundy and Veenhuizen, Proc. CIGR, Latest Dev. in Livestock Housing, Urbana, Ill., June 1987; Czarick and Van Wicken, ASAE Paper 85-4510, Winter MTG ASAE, Chicago, Ill., 1985) in animal housing. Repace et al. (Clinical Ecology, Volume 11 (2), 90-94, Winter 1983-1984) showed ionizers could accelerate the precipitation of smoke particles in an unventilated room by up to a factor of 18 or up to an equivalent ventilation rate of 6 air changes per hour.
Saurenman et al. (U.S. Pat. No. 3,696,791-Oct. 10, 1972) disclose the use of air ionization for reducing air-borne particulates and ammonia gas and odors in feeding enclosures of animals, especially poultry. Ions are dispersed into the feeding areas. The device includes a means to disperse ions suspended overhead, a static voltage sensor, a control device, a voltage generator, a blower, and a positively charged conductive grid.
Saurenman (U.S. Pat. Nos. 4,388,667['667]-Jun. 14, 1983; 4,390,923['923]-Jun. 28, 1983; and 4, 493,289['289]-Jan. 15, 1985) discloses devices for reducing air-borne particulates and ammonia gas and odors in feeding enclosures of animals, especially poultry, using air ionization. The '289 patent discloses a device with flexible cables containing an elongated and sidewardly penetratable metallic core to which voltage is applicable. The cable includes a protective sleeve of insulating material and needles having shanks penetrating through the sleeve and extending sidewardly adjacent the core to make electrical contact with the core so as to receive application of voltage in order to dispense ions into the atmosphere from tips exposed outwardly from the cable. The apparatus also includes a voltage generator and a control device. It is grounded so that negatively charged particles are attracted to deck surfaces. The '667 patent discloses an apparatus similar to the one disclosed in the '289 patent which applies positive voltage to one electrically conducive cable and negative voltage to a second electrically conducive cable in order to control static charge, eliminate arching, and control net ion flux in animal or poultry zones.
Saurenman (U.S. Pat. No. 4,326,454['454]-Apr. 27, 1982) discloses ion dispensers which are supported on an extended carrier that defines the electrostatically charged surfaces. An extended metallic surface, that can be grounded, may be associated with the carrier surface. This metallic surface may be defined by the wall of the chamber containing the dispenser.
While various systems have been developed for dust reduction, including reduction of airborne transmission of disease, there remains a need in the art for a more effective system for reducing dust levels which in turn reduces microbial contamination using negative air ionization with a ground plane for enhancement of ion generation. The system can also include a liquid dust collection system which does not lose efficiency with time, even when exposed to large concentrations of dust. The present invention is different from the related art systems.